A power switching device is a device comprising a pair of contacts that opens and closes an electrical circuit by opening or closing these contacts. When a fault current is detected, an interruption signal is input to the power switching device and in response to this interruption signal the power switching device separates the contacts so as to interrupt the current.
In addition, such a power switching device is typically provided with a pair of arc contacts and a buffer chamber or pressurizing chamber. These arc contacts accept the arc discharge (or electric arc) that is generated by separation of the contacts. The puffer chamber and/or pressurizing chamber comprise a piston and cylinder, and compress the gas present in the chamber by relative movement of the cylinder and piston, so that high-pressure gas from within the chamber can be directed between the arc contacts. The arc discharge is extinguished by this high-pressure gas blast, thereby completing current interruption.
The operating mechanism is provided in order to effect relative movement of the movable contact for such circuit switching, the arc movable contact, and the piston or cylinder. This operating mechanism is therefore required to be capable of being driven when desired, capable of high-speed movement of the movable element, and to provide excellent response of the movable element.
The reason why the operating mechanism is required to be capable of being driven when desired is that it is desirable to perform the interruption action with an appropriate timing, at which interruption can easily be effected, with reference to the variations in the conditions relating to extinction after generation of the fault current, because of the periodic fluctuation of the voltage, when the fault current is AC, or random fluctuations of phase when the fault current is generated. The reason why the movable element is required to be capable of high-speed movement and excellent response is that the interruption action must be completed in the short time of a few tens of msec from initiation of the interruption instruction.
Furthermore, in addition to such drive performance aspects, in view of progress with underground deployment of power equipment and drive mechanisms, restrictions are being demanded regarding the size of the operating mechanism and demands are being made in regard to maintainability.
Operating mechanisms that have currently been proposed include a pneumatic-type operating mechanism, a hydraulic-type mechanism, a spring type mechanism or an electromagnetic drive type mechanism. A hydraulic type mechanism is a type in which the movable section is driven using a hydraulic actuator. The spring system is a system in which the movable section is driven using energy obtained when a compressed spring is released, and is the system that is currently chiefly used. The electromagnetic drive system is a system in which the movable section is driven by an electromagnetic actuator.
The hydraulic system typically makes it possible to obtain large thrust and is advantageous for achieving high speed of operation. In view of the magnitude of the drive energy that can be obtained from a hydraulic mechanism, a hydraulic mechanism may be expected to be of smaller size than a spring mechanism; however, it does have the drawbacks that a hydraulic system is required including at least a hydraulic pump and accumulator and is subject to oil leakage and temperature dependence, making it unsuitable as a mechanism for use for example in cold regions.
The spring system is the system that is currently chiefly employed; this system is applicable in regions including for example cold regions since, compared with a hydraulic system, it does not suffer from oil leakage and has no temperature dependence. However, this system displays a high risk of failure when driven on multiple occasions, since it is complicated, being constructed of a large number of components and including a large number of sliding sections. This therefore involves a large amount of labor, since the maintenance frequency is high and the construction is complicated, with a large number of components. Thus the maintenance characteristics cannot be said to be advantageous, from the point of view of frequency and labor involved in maintenance. Furthermore, since spring force is utilized, the mechanism cannot be driven at will.
In contrast, the electromagnetic type is superior in terms of maintenance since its construction is straightforward, so the number of components and sliding sections is small. The speed of response to an electrical signal is also very high. Examples of the electromagnetic type of drive system include systems in which the movable contact is driven by directly converting the drive force of a rotary electrical machine, such as for example Laid-open Japanese Patent Application Tokkai 2009-212372 (hereinafter referred to as Patent Reference 1) or Laid-open Japanese Patent Application Tokkai 2008-021599 (hereinafter referred to as Patent Reference 2). In these systems, the operating mechanism can be driven at will by controlling the drive of the rotary electrical machine.
Also, as examples in which electromagnetic attractive force or electromagnetic repulsive force are directly employed as thrust, there may be mentioned systems utilizing the attractive force of an electromagnet and permanent magnet, such as for example Laid-open Japanese Patent Application Tokkai 2003-016888 (hereinafter referred to as Patent Reference 3), or systems utilizing electromagnetic attractive force or repulsive force acting on an air-core coil, for example Laid-open Japanese Patent Application Tokkai H 10-040782, Tokkai 2002-124158 (hereinafter referred to as Patent Reference 4 and Patent Reference 5), or systems utilizing induced repulsion, such as for example Laid-open Japanese Patent Application Tokkai H 11-025817 (hereinafter referred to as Patent Reference 6). When an air-core coil is employed, the characteristic advantages are obtained that the time constant of the electrical circuit is small and high response performance is obtained in initial operation.
Also, systems have been proposed in which cylindrical permanent magnets are employed that are held with a fixed mutual separation and arranged on the inside and outside: an exciting current is applied to an air-core coil that is arranged between these inside and outside cylindrical permanent magnets, thereby driving this air-core coil. Examples are Issued Japanese Patent Number 4625032 (hereinafter referred to as Patent Reference 7), or Laid-open Japanese Patent Application Number Tokkai 2010-154688 (hereinafter referred to as Patent Reference 8).
While various types of such electromagnetically driven operating mechanisms have been proposed, it has been remarked that they are inferior compared with hydraulic operating mechanisms or spring-type operating mechanisms in regard to thrust, which is actually indispensable for high-speed interruption and high-speed closure of the movable contact.
Specifically, although, in the examples using a rotary electrical machine indicated in Patent References 1 and 2, it is proposed to employ an iron core in the winding of the rotary electrical machine in order to obtain high torque, this results in large inductance and a large time constant of the electrical circuit, so there are limits to the extent to which response performance can be improved. There is therefore a trade-off between thrust and response.
Also, in the case of a system employing electromagnetic attraction or electromagnetic repulsion as in Patent References 3 to 6 as direct thrust, it is difficult to achieve drive at will in all operating regions, so it is difficult to achieve interruption action with appropriate timing such as to facilitate interruption.
In the case of a system employing an actuator in which a cylindrical permanent magnet is arranged as shown in Patent Reference 7, drive can be achieved at will, and no iron core is employed in the coil, so the inductance can be kept comparatively small.
However, in this Patent Reference 7, in order to generate more powerful magnetic flux and in order that the effects of the magnetic field should not reach the outside, a back yoke is employed, comprising cylindrical magnetic bodies outside the external cylindrical permanent magnet and inside the internal cylindrical permanent magnet: consequently, there is the problem that the inductance of at least the coil tends to be increased. Furthermore, if a powerful permanent magnet is employed in order to increase thrust, the back yoke must be made of large thickness, in order to avoid magnetic saturation of the back yoke. Consequently, even if a powerful permanent magnet was employed, it was difficult to reduce the thrust/volume ratio.
In contrast, in the case of the linear actuator of Patent Reference 8, a construction is adopted in which a back yoke is not required, by a special arrangement of permanent magnets, so that the magnetization vector varies in a periodic fashion. The actuator can therefore be said to be capable of being driven at will, having light weight and excellent response performance. By employing this actuator as the operating mechanism of a power switching device, excellent interruption performance should be obtained.
However, although the linear actuator of Patent Reference 8 has light weight and excellent response, and is capable of being driven at will, due to the actual construction of a linear actuator, it requires a linear guide to guide the movable element in the drive axis direction. Consequently although the linear actuator has excellent maintainability compared with the hydraulic type or spring type, such a linear guide tends to lower maintainability.
Also, a linear guide tends to increase bulk and raise costs. Furthermore, it tends to have an adverse effect in terms of improving operating speed, since it increases the weight of the movable section of the linear actuator.
As described above, although various electromagnetic operating mechanisms have previously been proposed for a power switching device, and these offer excellent drive performance, it cannot be said that the limit has been reached in terms of ease of maintenance of an electromagnetic system.
The present invention was made in order to solve these problems, its object being to provide an electromagnetic operating mechanism and power switching device provided therewith that does not require a mechanical guide and that has excellent maintainability.
In order to achieve the above object, the present invention is constructed as follows. Specifically, an operating mechanism for a power switching device for mutually shifting an opening/closing device between an interrupted condition and closed condition by reciprocating drive of a movable contact comprises: a first row of permanent magnets; a second row of permanent magnets; a double cylinder; a floating output ring; and exciting means.
The first row of permanent magnets is constituted by arranging annular or arcuate permanent magnets adjacently so that the magnetic poles of these permanent magnets are rotated by a maximum of 90° in each case in a cross-sectional plane including their central axes. The second row of permanent magnets is also constituted by arranging annular or arcuate permanent magnets adjacently so that the magnetic poles of these magnets are rotated by a maximum of 90° in each case in a cross-sectional plane including their central axes.
The double cylinder is fixed so that the two rows maintain a fixed distance, with said first permanent magnets and said second permanent magnets, whose magnetization vector radial components are in the same direction, facing each other. The floating output ring is arranged with a coil constituted by a conductor wound thereon, between said first row of permanent magnets and said second row of permanent magnets, and has no mechanical restraining relationship with other members, apart from being directly or indirectly linked with said movable contact.
The exciting means generates current for exciting said coil. This exciting means comprises supporting force control means and thrust control means. The supporting force control means keeps the central axes of said double cylinder and said floating output ring coincident by generating supporting force for said floating output ring by magnetism, by controlling the d axis current component of said exciting current. The thrust control means generates axial thrust between said double cylinder and said floating output ring by controlling the q axis current component of said exciting current.
Said double cylinder may comprise: a disc that links the tubes of this double cylinder at the end face thereof and that fixes the distance of these tubes; an aperture provided on said disc and through which said floating output ring passes; and a low friction resin section that offers low friction with respect to said floating output ring, and is provided at the edge of said aperture.
Also, said double cylinder may comprise: a disc that links the tubes of this double cylinder at the end face thereof and that fixes the distance of these tubes; an aperture provided on said disc and through which said floating output ring passes; and said floating output ring may comprise a low friction resin section in the circumferential surface region through which said aperture passes.